Motor vehicle heat exchanger system

ABSTRACT

A motor vehicle heat exchanger system with a closed circuit for an operating medium includes an evaporator for evaporating the operating medium and a condenser for condensing the vaporous operating medium AM is provided. A reservoir for the liquid operating medium is integrated between the condense and the evaporator. Liquid operating medium is conducted from the reservoir via a feed line into the evaporator. In addition the reservoir and the evaporator are connected with each other via a compensation line. Vapor which may form during operation of the motor vehicle heat exchanger system on the liquid side of the evaporator can escape through the compensation line thereby achieving a pressure compensation.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the priority of German Patent Application, Serial No. 10 2015 107 442.7, filed May 12, 2015, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference in its entirety as if fully set forth herein.

BACKGROUND OF THE INVENTION

The present invention relates to a motor vehicle heat exchanger system.

The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.

The use of waste heat or lost thermal energy in motor vehicles, for example of lost thermal energy in the exhaust gas of the internal combustion engines of motor vehicles, offers several possibilities to increase the efficiency of motor vehicles. In this connection the use of waste heat for heating the passenger compartment offers the possibility to dispense with additional heating measures thereby reducing fuel consumption. The waste heat can also be used for accelerating the warm-up of drive components of a motor vehicle during startup. Hereby mechanical power loss and with this motor load and consumption during the warm-up phase can be reduced.

The recovery of waste heat generated during combustion processes of the motor thus offers a great potential to safe fuel and can contribute to increasing the comfort of driving and using a motor vehicle.

The references EP 0 832 411 B1 or DE 696 06 296 T2 disclose a method for transporting liquids in a micro fluid circuit system with a capillary pump for transporting heat. In the circuit at least one evaporator and a condenser and a container for receiving a heat transmitting fluid or operating medium is provided. The evaporator has an outlet, which is connected with the inlet of the condenser via an evaporating line. An outlet of the condenser is connected with the storage container. The evaporator contains an evaporator body with a permeable material in order to evaporate the operating medium by heat absorption and to generate a capillary pump pressure in the interior of the circuit. The reservoir and the evaporator are thermally isolated against each other and are connected with t each other by a line. Hereby the container is constructed so that it is held at a lower temperature than the evaporator. This is intended to enable a heat exchange with a minimal temperature difference between the heat source and the condenser.

The reference U.S. Pat. No. 4,087,047 A or DE 25 23 645 A1 and also DE 38 06 418 C2 disclose proposals in which the cooling water is to be heated with so called heat pipes in an accelerated manner. Hereby conventional heat pipes are used, wherein the evaporator region of the heat pipe is in contact with the exhaust gas and the condenser part is in contact with the cooling circuit of the motor. The heat pipes have at their wall a capillary structure, which transports the operating medium from the condenser back onto the evaporator zone.

Further a heat pipe of the circuit type is part of the state of the art as disclosed in DE 10 2008 007 726 A1. This heat pipe is intended to conduct heat from the exhaust gas to an air cooled condenser. Via the condenser the air flowing into the driver compartment is heated.

A loop heat pipe is an evacuated closed heat transport system that is filled with operating medium. When using exhaust gas heat by means of loop heat pipes (LHP) LHP evaporators are integrated in to the exhaust gas line of motor vehicles. The evaporator consists essentially of a housing an inner capillary structure, a sealing and a cover. The sealing severs for maintaining a pressure difference between liquid and gaseous operating medium, which is generated by capillary forces in the capillary structure.

The evaporation in the capillary structure is enabled by the heat conductivity of the mostly metallic structure. At the same time the capillary structure acts as a heat bridge to the evaporator par in which the operating medium in a liquid state meets the capillary structure. In this evaporator part the heat bridge causes evaporation of the operating medium. This leads on one hand to a reduction of the pressure difference between the liquid part of the evaporator and the evaporation region. In addition the vapor pressures through the connection line between the reservoir and the evaporator, which impedes the supply of liquid operating medium and is characterized by a rising of vapor bubbles in the reservoir. At high heat input this effect can be so strong that the return flow is not sufficient to prevent the capillary structure from completely drying out. In this case the circuit inside the loop heat pipe is interrupted and the heat transport between the evaporator and the condenser comes to a halt.

It would therefore be advantageous and desirable to provide an improved motor vehicle heat exchanger system regarding its applicability and to increase its efficiency.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a motor vehicle heat exchanger system with a closed circuit for circulating an operating medium, includes an evaporator for evaporating liquid operating medium to vaporous operating medium; a condenser for condensing the vaporous operating medium; and a reservoir for receiving the liquid operating medium, wherein the reservoir is arranged between the condenser and the evaporator, wherein the reservoir and the evaporator are connected with each other via a feed line for conduction of liquid operating medium, and wherein the reservoir and the evaporator are further connected with each other via a compensation line.

The motor vehicle heat exchanger system has a closed circuit for an operating medium. In the circuit an evaporator is integrated, the evaporator is in heat conducting contact with a heat source of the motor vehicle. Particularly advantageously the evaporator is integrated in the exhaust gas stream of the internal combustion engine of the motor vehicle. This allows using the waste heat of the hot exhaust gas. The exhaust gas conducted out of the internal combustion engine of the motor vehicle is for this purpose completely or partially conducted though an exhaust gas duct, in the evaporator the operating medium is evaporated and form there flows via a vapor line to a condenser arranged in the motor vehicle. In the condenser a heat exchange with a user takes place, wherein the vaporous operating medium is condensed and liquefied. Via a return line the liquid operating medium is conducted into the reservoir and from there it is conducted back into the evaporator via the feed line.

The reservoir serves for storing operating medium and for homogenizing circulation of the operating medium. The reservoir is integrated between the condenser and the evaporator and connected with these via fluid lines. Hereby the reservoir and the evaporator are in contact with each other via a feed line for liquid medium.

The additional compensation line between the liquid part or the liquid side of the evaporator and the reservoir supports the vapor discharge from the liquid side of the evaporator or supports a pressure compensation from the evaporator toward the reservoir.

According to another advantageous feature of the invention, the evaporator includes at least one evaporator cassette, wherein in the evaporator cassette a capillary structure is arranged. In the evaporator cassette a liquid side and a vapor side are separated from each other by the capillary structure. Further an evaporator cassette has a vapor collector. in the vapor collector the vaporous operating medium is collected and form there conducted out of the condenser.

According to another advantageous feature of the invention, the capillary structure is formed by a porous plate body. Preferably the capillary structure is made of a sintered material. In particular the capillary structure is metallic.

According to another advantageous feature of the invention, the compensation line is connected with the liquid side of the evaporator cassette.

According to another advantageous feature of the invention, the compensation line is connected to the evaporator via a compensation connection and the feed line is connected to the evaporator via a feed connection. Hereby the compensation connection is n particular positioned above the feed connection. In this way the compensation connection is located in the motor vehicle heat exchanger system higher than the feed connection. As a consequence potential vapor, which may form on the liquid side, flows due to the natural buoyancy in the direction toward the compensation connection.

Liquid operating medium is conducted via the feed line between the reservoir and the evaporator in the lower part of the evaporator, whereas the vapor is discharged from the upper part of the evaporator via the compensation line. As a result of this arrangement the liquid operating medium pushes the vapor generated on the liquid side upwards from where the vapor is discharged in the direction of the reservoir via the compensation line. This results in a forced direction for the vapor. A rising of vapor bubbles through the feed line between the reservoir and the evaporator is prevented. Particularly advantageously is hereby that on the liquid side no large vapor bubbles or vapor regions are generated. Such disadvantageous regions may lead to an overheating of the operating medium and in critical cases to damage because there the liquid operating medium with the corresponding cooling effect is missing.

An evaporator cassette is preferably configured rectangular and plate-shaped. In a simple construction the housing consists of an evaporator cassette made of a housing shell, which is closed by a lid. In the lid the required connections for the operating medium as wells as for the compensation line are integrated. In the interior of the evaporator cassette the capillary structure is integrated which is also configured rectangular plate-shaped. This configuration is advantageous in terms of manufacture. The same applies to the required mounting space and to the weight of the evaporator. In the capillary structure vapor grooves or vapor channels are formed. Particularly preferably the vapor grooves or vapor channels are provided on the vapor side of the capillary structure. Alternatively or in addition vapor grooves or vapor channels can also be formed in the housing of an evaporator cassette namely on the vapor side in the bottom of the housing. Such vapor grooves or vapor channels can be formed by embossments in the bottom of the housing. Of course the vapor grooves or vapor channels can also be formed by a material removing processing.

According to another advantageous feature of the invention, the evaporator has at least two evaporator cassettes wherein between the evaporator cassettes a channel for conducting a hot fluid in particular an exhaust gas channel is formed. The heat transfer form the hot fluid in particular from the exhaust gas into the evaporator, is accomplished via heat transfer elements, for example heat exchanger fins. As a result of the heat input the operating medium evaporates inside the capillary structure and is conducted through vapor grooves to a vapor collector and subsequently through a vapor line to a condenser. In the condenser the operating medium is liquefied by heat dissipation and flows via a return line into the reservoir. Form the reservoir the liquid operating medium flows via the feed line back to the evaporator.

In the condenser of the motor vehicle heat exchanger system according to the invention the vaporous operating medium, which comes form the evaporator is condensed. For this the condenser is integrated in a cooling fluid stream and is impinged with cooling fluid, wherein the cooling fluid flows against the condenser is a or flows around or through the condenser. In a configuration of the motor vehicle heat exchanger system which is advantageous in praxis the reservoir can be arranged in the cooling fluid stream and is cooled by the cooling fluid stream. This measure contributes to maintaining a low pressure level in the circuit.

BRIEF DESCRIPTION OF THE DRAWING

Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:

FIG. 1 shows a technically simplified and schematized longitudinal section through an evaporator cassette of a heat exchanger of the motor vehicle heat exchanger system according to the invention;

FIG. 2 shows the evaporator cassette of FIG. 1 with the illustration of fluid flows; and

FIG. 3 shows a technically simplified illustration of a motor vehicle heat exchanger system according to the invention with the essential system components.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Throughout all the Figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.

A motor vehicle heat exchanger system has a closed circuit for an operating medium AM and includes an evaporator 1 for evaporating the operating medium AM and a condenser 2 for condensing the vaporous operating medium AMd the operating medium AM is in particular ethanol. Between the condenser 2 and the evaporator 1 a reservoir 3 is provided. The evaporator is integrated in the exhaust gas stream AG of an internal combustion engine of a motor vehicle.

The evaporator 1 includes in the exemplary embodiment according to FIG. 3 a total of two evaporator cassettes 4. FIGS. 1 and 2 show a technically simplified longitudinal sectional view of an evaporator cassette 4.

The evaporator cassettes 4 are configured rectangular with housing 5 made of a housing shell 6 and a cover 7. In the housing 5 of the evaporator cassettes 4 a respective capillary structure 8 is arranged. The capillary structure 8 is formed by a porous plate body made of a sintered material, in particular in metal basis. The capillary structure 8 is aligned with the housing 5 and is sealed against the cover 7 via spacers 9. The spacer 9 are formed by gaskets.

The two evaporator cassettes 4 are arranged parallel to each other and are oriented vertically. Between the evaporator cassettes 4 an exhaust gas channel 10 for hot exhaust gas Ag is formed. The exhaust gas AG originates form the exhaust gas stream of the internal combustion engine of the motor vehicle. This can be a partial stream derived form the exhaust gas stream. In the exhaust gas channel 10 heat transfer elements 11 for enlarging the heat transfer surface are provided. The heat transfer elements 11 are sheet metal lamellas that are oriented in longitudinal direction of the evaporator 1, so called heat exchanger fins. The exhaust gas AG flows though the exhaust gas channel 10. Hereby heat is transferred from the exhaust gas AG to the evaporator cassettes 4 and the operating medium AM. The heat flux is illustrated in FIG. 2 by the arrows W. In FIG. 2 also the fluid flow of liquid operating medium AM and vaporous operating medium AM is shown. For indicating the aggregate state of the operating medium AM liquid operating medium is designated AMf and vaporous operating medium AMd.

In an evaporator cassette 4 a liquid side 12 and a vapor side 13 are separated by the capillary structure 8. On the liquid side 12 a feed line 14 via a feed connection 15 for supplying liquid operating medium AMf into the evaporator cassette 4 is provided. Each evaporator cassette 4 further has a vapor collector 16. In the vapor collector 16 the respective operating medium AMd evaporated in an evaporator cassette 4 is collected and conducted in the circuit of the motor vehicle heat exchanger system to the condenser 2 via a vapor outlet 17 and a vapor line 18.

The liquid operating medium AMf is distribute on the liquid side 12 via the surface of the capillary structure 8. As a result of heat transfer from the exhaust gas AG that flows through the exhaust gas channel 10 the operating medium AM is evaporated in the evaporator cassettes 4, the operating medium AM traverses the capillary structure 8 form the liquid side 12 and transitions form the liquid state into the vaporous state. The phase boundary between liquid and vapor during operation of the evaporator 1 extends in the capillary structure 8, whereby a capillary pressure is generated which causes and maintains the circuit of the operating medium AM. On the vapor side 13 the vaporous operating medium AMd flows through vapor grooves 19 until it enters the vapor collector 16. The vaporous operating medium AMd is discharged form the vapor collectors 16 via the vapor outlet 17 and the vapor line 18.

The operating medium AMf which has been liquefied in the condenser 2 as a result of heat given off to a user is conducted via a return line 20 into the reservoir 3. From the reservoir 3 the liquid operating medium AMf reaches the evaporator 1 via the feed line 14 and is conducted into the evaporator cassettes 4.

Between the evaporator 1 and the reservoir 3 a compensation line 21 is additionally provided which connects the reservoir 3 and the evaporator 1. Via the compensation line 21 pressure compensation takes place between the evaporator 1 and the reservoir 3. This in particular allows air bubbles, which form on the liquid side 12 of the evaporator, to escape.

FIG. 3 shows the fluid flow of liquid operating medium AMf and vaporous operating medium AM in the circuit of the motor vehicle heat exchanger system. Liquid operating medium AM is stored in the reservoir 3 and is conducted via a respective feed line 14 to the evaporator 14. For supplying the two evaporator cassettes 4 the feed line 14 is divided into two line branches. Via the feed connection 15 the liquid operating medium AM reaches the liquid side 12 of the evaporator cassettes 4. Evaporated or vaporous operating medium AMd exits from the evaporator cassettes 4 via the vapor outlets 17 and is conducted to the condenser 2 via the vapor line 18.

The compensation line 21 is also connected with the liquid side 12 of an evaporator cassette 4 via the compensation connection 22. It can be seen that the compensation connection 22 is arranged above the feed connection 15. The compensation connection 22 is thus situated vertically above the feed connection 15. As a consequence the liquid operating medium AMf is conducted via the feed line 14 into the lower part of the evaporator 1 or the evaporator cassettes 4 and evaporates as described above, wherein the operating medium AM hereby traverses the capillary structure 8 from the liquid side 12 to the vapor side 13. When operating medium AM evaporates in the liquid side 12 by heat bridge formation, the vapor can be conducted out of the upper part of the evaporator 1 or the evaporator cassettes 4 via the compensation line 21. The liquid operating medium AM pushes the vapor generated on the liquid side 12 upwards which it is discharged via the compensation connection 21 and is conducted into the reservoir 3 through the compensation line 21. The formation of vapor bubbles or vapor regions on the liquid side 12 of an evaporator cassette 4 can thus be prevented or counteracted.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: 

What is claimed is:
 1. A motor vehicle heat exchanger system with a closed circuit for circulating an operating medium, said heat exchanger system comprising: an evaporator for evaporating liquid operating medium to vaporous operating medium; a condenser for condensing the vaporous operating medium; and a reservoir for receiving the liquid operating medium, said reservoir being arranged between the condenser and the evaporator, wherein the reservoir and the evaporator are connected with each other via a feed line for conduction of liquid operating medium, and wherein the reservoir and the evaporator are further connected with each other via a compensation line.
 2. The motor vehicle heat exchanger system of claim 1, wherein the evaporator comprises at least one evaporator cassette, wherein a capillary structure is arranged in the evaporator cassette and the evaporator cassette has a liquid side and a vapor side and a vapor collector.
 3. The motor vehicle heat exchanger system of claim 2, wherein the compensation line is connected with the liquid side of the at least one evaporator cassette.
 4. The motor vehicle heat exchanger system of claim 1, wherein the compensation line is connected to the evaporator via a compensation connection and the feed line is connected with the evaporator via a feed connection, said compensation connection being positioned above the feed connection.
 5. The motor vehicle heat exchanger system of claim 2, wherein the capillary structure is formed by a porous plate body made of a sintered material.
 6. The motor vehicle heat exchanger system of claim 1, wherein the capillary structure has vapor grooves and/or vapor channels on the vapor side.
 7. The motor vehicle heat exchanger system of claim 1, wherein the evaporator has at least two evaporator cassettes, and wherein a channel is formed between the at least two evaporator cassettes.
 8. The motor vehicle heat exchanger system of claim 7, wherein the channel is an exhaust gas channel.
 9. The motor vehicle heat exchanger system of claim 7, further comprising heat transfer elements provided in the channel.
 10. The motor vehicle heat exchanger system of claim 2, wherein on the vapor side of an evaporator cassette vapor grooves and/or vapor channels are provided in the bottom of the housing of the evaporator cassette. 